Solar receiver tube assembly with suited receiver tube per working temperature and use of the receiver tube assembly

ABSTRACT

A solar receiver tube assembly is provided with at least one first solar receiver tube with a first selective absorptive coating; at least one second solar receiver tube with a second selective absorptive coating, wherein values of at least one optical characteristic of the first selective coating and the second selective coating differs from each other while an operating the solar receiver tube assembly. The optical characteristics are preferably α and ε. The idea is to improve the effectiveness of the receiver tubes along the receiver assembly.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to PCT/EP2012/070242, having a filing date of Oct. 12, 2012 and of EP application number 11186183.7, the entire contents of both which are hereby incorporated by reference.

FIELD OF TECHNOLOGY

The following relates to a solar receiver tube assembly and a use of the receiver tube assembly.

BACKGROUND

A solar field comprises loops with receiver tubes for absorbing solar energy and transferring absorbed energy to a heat transfer fluid (HTF) which is located in the receiver tubes. One loop or more than one loop is a solar receiver tube assembly.

A receiver tube comprises a selective absorptive coating. The selective coating set point is a tradeoff between maximum absorption and minimal radiation. It is the nature of the selective coating that enlarging the absorption percentage (designated by α) will increase the radiation (designated by ε). It is also in the nature of the selective coating that while the absorption is indifferent with the working temperature, the emissivity is higher as the temperature is higher. In the current state of the art all the receivers along the loop have the same design.

SUMMARY

An aspect relates to providing an optimized solar receiver tube assembly.

A further aspect relates to a use of the solar receiver tube assembly.

These are achieved by the invention specified in the claims.

A solar receiver tube assembly is provided with at least one first solar receiver tube with a first selective absorptive coating; at least one second solar receiver tube with a second selective absorptive coating, wherein values of at least one optical characteristic of the first selective coating and the second selective coating differs from each other while an operating the solar receiver tube assembly. The optical characteristics are preferably α and ε. The idea is to improve the effectiveness of the receiver tubes along the receiver assembly.

The advantage is by gaining more energy from the loop and the solar field as a whole especially at the area where the temperature is low and the threshold between absorption and suppression can be shifted to higher wave length and gain more energy. This will become more effective when working in higher temperature HTF for example molten salt or direct steam generation (DSG).

In an embodiment the first receiver tube and the second receiver tube are components of a single loop of the solar receiver tube assembly. By this, within a loop different solar receiver tubes are used. Alternatively, same kinds of receiver tubes with same selective absorptive coatings are used, whereas while the operating the complete system the values of the optical characteristics are different.

Concerning a different embodiment the first receiver tube is a component of a first loop of the solar receiver tube assembly and the second receiver tube is a component of a second loop of the solar receiver tube assembly and the first loop and the second loop are different from each other. There are at least two loops.

Finally the solar receiver tube assembly is used in a power plant for converting solar energy into electrical energy.

BRIEF DESCRIPTION

Some of the embodiments will be described in detail, with references to the following figures, wherein like designations denote like members, wherein:

FIG. 1 and FIG. 2 show partial views of different solar receiver tube assemblies.

DETAILED DESCRIPTION Example 1

More than one type of solar receiver tubes with different set point are installed on different locations along one single loop 100 of the solar receiver tube assembly 1 (FIG. 1). There are at least one first solar receiver tube 101 with a first selective absorptive coating and at least one second solar receiver tube 102 with a second selective absorptive coating.

Values of at least one optical characteristic of the first selective coating and the second selective coating differ from each other while an operating the solar receiver tube assembly. The set point for lower temperature associated with the beginning of the loop might have higher α and higher ε and the receiver associated with the end of the loop and higher temperature will be design with lower ε and lower α.

Example 2

The result concerning example 1 is possible with different loops 200 and 300 for different temperature. For instance, this is suggested for direct steam generation (DSG). In this case different loops will be equipped with different solar receiver tubes.

In view of the invention there are at least two possibilities to gain the different values of the optical characteristics:

Using solar receiver tubes with different solar absorptive coatings.

Development of a special coating, using thermal sensitive layers, that is changing its optical characteristic according its temperature. In this case the entire loop or the entire field will be equipped with the same receiver tubes but the optic behaviour of the selective coatings will be effect by the temperature of the receiver tubes. 

The claims are as follows:
 1. A solar receiver tube assembly with at least one first solar receiver tube with a first selective absorptive coating; at least one second solar receiver tube with a second selective absorptive coating, wherein values of at least one optical characteristic of the first selective coating and the second selective coating differs from each other while operating the solar receiver tube assembly.
 2. The solar receiver tube assembly according to claim 1, wherein the first receiver tube and the second receiver tube are components of a single loop of the solar receiver tube assembly.
 3. The solar receiver tube assembly according to claim 1, wherein the first receiver tube is a component of a first loop of the solar receiver tube assembly and the second receiver tube is a component of a second loop of the solar receiver tube assembly and the first loop and the second loop are different from each other.
 4. The use of the solar receiver tube assembly according to claim 1 in a power plant for converting solar energy into electrical energy. 